The present invention relates to a lung ventilator used for maintaining or assisting respiration and particularly to a small-sized and lightweight lung ventilator which is able to be used for a moderate or slight respiration disorder patient and suitable for use in a sickroom, at home, or in an ambulance for other than a serious respiration disorder patient requiring care in an intensive care unit.
In this kind of simple lung ventilator, a piston type pump is conventionally used as a means for supplying inspiration gas to a patient.
FIG. 1 is an illustration showing the constitution of the conventional gas supply pump and FIG. 2 is a graph showing a change in the airway pressure of a patient during inspiration by denoting time (second) in the abscissa and airway pressure (Paw) of a patient in the ordinate.
In FIG. 1, numeral 30 indicates a flexible bellows made of rubber or other materials, 31 a Suction valve, 32 an outlet valve, 33 a piston, 34 a screw, 35 a motor, 36 a rotary encoder, and 37 a position sensor for controlling the expanded and contracted positions of the rubber bellows 30. Namely, the gas supply pump of the conventional lung ventilator is a piston type pump, in which the rotating motion of the motor 35 is changed to linear reciprocating motion of the piston 33 so as to suck or eject gas by expansion or contraction of the rubber bellows 30.
In this gas supply pump system, a pressure sensor (not shown in the drawing) detects a reduction in the pressure in the respiration circuit when a patient starts inspiration and sends an operation start signal to the motor 35. However, the time lag between the start of rotation of the motor 35 and actual arrival of inspiration gas at the patient is great, therefore the airway pressure of the patient is changed to negative pressure, as indicated by portion M as shown in FIG. 2 during this period. This is a load in respiration work for the patient, which is contrary to the original purpose of the lung ventilator, i.e., reducing the respiration workload.
As a solution for the above problem, a continuance flow type lung ventilator is known.
FIG. 3 is a flow diagram showing the constitution of the conventional continuance flow type lung ventilator.
In the lung ventilator shown in FIG. 3, air which is ejected from an air compressor 1A via an air pressure regulator 40, and oxygen which is supplied from a separated oxygen source (not shown in the drawing) via an oxygen pressure regulator 41, are blended by an oxygen blender 42 so as to adjust the oxygen density and provide for the continuance flow. The flow rate of the continuance flow is adjusted by a flow controller 43, and which is supplied to the patient.
In the case of spontaneous breathing, the patient breathes freely and gas expired by the patient is exhaled through an exhalation valve 10. A pressure meter 13 and an inspiration safety valve 14 are installed in the inspiration circuit so as to insure the safety of the lung of the patient in the inspiration pressure applied thereto.
Flow lines branching from the inspiration circuit are installed, to which are equipped with such as a three-way solenoid valve 11A, a PEEP (positive expiratory end pressure) valve 12A, and a PEEP adjustment valve 44 so as to open or close the exhalation valve 10.
In this continuance flow type lung ventilator, the exhalation valve 10 is usually opened so as to continuously supply the inspiration flow required by a patient, thereby the patient breathes freely. When it is necessary to forcibly apply pressure to the lungs of the patient, the exhalation valve 10 is closed during the period of that time.
In the conventional continuance flow type lung ventilator shown in FIG. 3, there is a problem that when it is necessary to increase oxygen density in the inspiration flow, for example, when the inspiration flow rate is 30 l/min and the oxygen density is 100%, an oxygen flow of the rate of 30 l/min is continuously necessary, and the consumption of oxygen is high. Therefore, any home oxygen concentrator for home use having an oxygen gas flow rate from 5 to 6 l/min is not sufficient to supply the necessary large quantity of oxygen.
Namely, in a continuance flow type lung ventilator of the prior art, the inspiration gas of air and oxygen to be supplied is made constant in pressure by the respective pressure regulators, and then the flow rate thereof is controlled, so that the performance required for the air compressor comes up to operational pressure of 2 to 3 kg/cm.sup.2 and a maximum flow rate of 100 l/min. Therefore, the air compressor meeting these conditions requires a motor of 100 to 200 W. However, it is impossible for a battery to drive such motor because it is too large and heavy.
As shown in FIG. 3, the lung ventilator requires the air pressure regulator 40, the oxygen pressure regulator 41, the oxygen blender 42, and the flow controller 43, and there is a problem that it is contrary to the requirements for a lung ventilator, i.e., small-sized, lightweight, and simple operation.